Both investment casting and centrifugal casting can produce high-quality, near-net-shape parts. One of the key differences is that investment casting utilizes one-use ceramic molds that are broken off the cooled parts, while centrifugal casting employs permanent dies that are reused. In addition, centrifugal casting dies are spun at high RPMs to achieved designed casting properties. Investment casting is a static process that relies on gravity to flow the alloys.
Some may think that the process is called “investment” casting because of the up-front investment in tooling that is required – a very good investment in many cases. But in actuality, the term comes from the processes itself. To create the molds that will receive molten alloy and form parts, wax patterns are dipped into a ceramic slurry, which adheres to the patterns in layers that form the molds. Dipping an object in a liquid, which then sticks to the surface of the object is referred to as “investing,” thus the name.
Aerospace Material Standards (AMS) are a set of rigorous requirements that have been established to ensure that materials, components and devices meet the special design and safety needs of the aerospace and aircraft industries. Thermal, optical, mechanical, chemical and electrical properties are covered by these standards. It is critical that foundries producing precision cast parts for these applications comply with AMS. This takes a thorough understanding of and commitment to AMS, a high level of foundry expertise and the appropriate casting equipment and testing instruments.
Investment casting is an exceptionally good choice for parts that go into pumps for a virtually endless variety of industries. Whether the application requires aluminum, stainless steel, brass, copper, bronze, iron or numerous other common and specialty alloys, investment casting can produce the parts efficiently, precisely and with a level of quality few other processes can match. It can achieve the exacting specifications required of precision cast parts for both pneumatic and hydraulic equipment, with the consistency that is absolutely essential. Investment casting also provides long-term cost-effectiveness, especially for large part runs.
The term ISO (International Standards Organization) and ISO certifications are often mentioned, but why is it important for precision cast parts and the investment casting process? ISO comprises guidelines and tools that assure customers of the foundry’s safety, reliability and quality. ISO certification means that the castings are produced efficiently and in conformity with industry best practices. This positively impacts production cost, casting quality, parts consistency, delivery reliability and overall value.
Achieving the desired quality and specifications for precision cast parts is essential for many industries and applications. While the investment casting process produces among the highest quality, most accurate parts, it is still imperative to test the castings to ensure the proper results. There are many different testing processes, from relatively simple and straightforward, such as the tensile or break tests, to highly advanced technical tests, like spectrographic analysis. Each measures or assesses a specific characteristic or property of the casting. A foundry should have these testing capabilities to make sure the castings they produce are to spec and top quality. It should also have the expertise on staff to select and administer the right test for each situation.
Finished, inspected castings are ready to be securely packaged and shipped to the customers in accordance with their preferences. In addition to standard fulfillment ad shipping, special programs may be available for enhanced inventory management. An example is a zero-days lead time stocking – or consignment – program, which allows customers to access specified components when needed and pay when they are used rather than when the castings are shipped.
Before castings leave the foundry, they are subject to high-tech testing and inspection to ensure that they meet the necessary standards and specifications. This is a crucial step in the production process because it can detect deficiencies that may not be visible to the eye. Depending on customer preferences, a wide range of non-destructive testing is available from ultrasonic testing, spectrographic analysis and corrosion testing to mechanical testing, radiographic testing (RT), magnetic particle inspection (MPI) and much more.
The castings are now ready for any finishing work that is required. One of the biggest advantages of the investment casting process is that it produces “near-net-shape” parts that typically need little or no finishing work. This saves time, reduces cost, expedites production and increases the consistency of the castings. If finishing work is required, it usually involves removal of excess metal, polishing the surfaces, heat treating and other such processes.
Once the castings – still within their molds – have completely cooled, they are transferred to the knockout department. Here, the ceramic shells that comprise the molds are broken off utilizing powerful jackhammer-like tools. This loud and intense process frees the newly cast parts and leaves the ceramic rubble to be discarded.
With the molds ready to be filled, the desired alloy is heated to its molten state. This temperature widely varies for different alloys and can exceed 3000º F. The molten alloy is then poured into the molds, ensuring that each is properly filled. This process must be carefully managed and monitored to avoid faults and irregularities in the castings. Improper temperature, poor fills and many other issues can compromise the finished castings.
After the dipping and coating step in the investment casting process, a structure now exists consisting of wax-filled shells or molds and the sprue that attaches them to a single entry point for molten metal. To remove the wax from the shells and clear the sprue, the molds are briefly placed in an 1,800º furnace. After cooling on a bed of sand, they are ready for pouring. Quality assurance is essential to avoid an array mold issues that can compromise the quality and accuracy of finished castings.
The dipping and coating step in the investment casting process is one of the most crucial in ensuring the quality, consistency and accuracy of finished castings. The sprue assembly is repeatedly dipped/coated with successive layers of ceramic and stucco to build up a solid shell that will be the mold for the castings. Traditionally, this can be done hand, requiring much experience and skill. Today, robotic dipping is rapidly growing as the preferred technology. Advanced robotics enhances the repeatability, efficiency and dependability of the shell/mold-making step in investment casting.
The second step in the investment casting process is creating the pattern assembly. In the vast majority of casting runs, more than one part can be cast at a time for efficiency and speed. To accomplish this, two or more (often many) patterns are attached to the sprue, which is a structure that will enable molten metal to be poured into multiple cavities from a single entry point. Craftsmen skillfully assemble the structure using hot wax to optimally place each pattern.
After designing the desired part with exact specifications, the investment casting process begins. Often, a prototype is created to ensure that the part specifications meet the application’s needs. Next, a tool is build that matches those exact specifications. The tool contains a cavity that is then filled with wax to create a pattern that holds the precise dimensions of the finished parts to be cast. While the tooling is one of the most costly aspects of investment casting, it is actually an excellent investment for longer runs. It can be used to make many finished castings.
Investment casting is an excellent choice for making precision cast parts for an almost limitless variety of components, applications and industries. A clear understanding of investment casting is helpful in determining whether it is best for any specific application.
Pennsylvania Precision Cast Parts utilizes a nine-step process to produce castings from an extensive range of common and specialty alloys in sizes up to 250 pounds. The steps include:
- Tooling and Pattern Making
- Pattern Assembly
- Dipping and Coating
- De-Waxing and Firing
- Testing and Inspection
- Packing and Shipping
Other foundries may use somewhat different steps, but the process is basically the same. Check back for a series of posts providing more detail on each of the investment casting process.
When it comes to customer orders at PPCP, Rita Williams is an invaluable link in the production chain. In fact, without Rita, there would be no chain. One of her most important responsibilities is to convert customer purchase orders into PPCP work orders. To fill this essential role, she has become an expert on how the production process works. In addition to order initiation, Rita work closely with customers, providing pricing, delivery schedules and more. Rita joined the PPCP team in 1988.
Making the best use of every resource and realizing the best possible ROI are essential in today’s manufacturing world, and precision casting is no exception. When choosing an investment casting partner, explore the foundries to determine if they are utilizing innovative processes and programs to maximize efficiency, productivity, quality and value. Look for advanced production management and quality systems that drive product, not just assess it. On-time performance (OTP) expectations, low-defect rate expectations, Kanban delivery programs, just-in-time (JIT) delivery programs, on-demand stock programs and other such initiatives will suggest that the foundry is on the leading edge of the industry.
Parts, equipment and components utilized in maritime industries encounter uncommon challenges. Highly corrosive seawater, hard usage and other punishing conditions can make standard materials and processes insufficient. Precision cast parts made through the investment casting process can utilize specialized alloys that can withstand the rigorous challenges of maritime conditions and usage far better than other options. Alloys can be custom made to exhibit the exact properties that are needed. Investment casting’s near-net-shape process also virtually eliminates costly finishing, making it economical, as well.
The investment casting process can produce exceptional quality, highly precise parts for a limitless range of applications and industries. Achieving such precision can get loud, however. One of the steps in the investment cast process is called “knockout.” This is when the ceramic shell is broken off of a recently poured and cooled casting. It gets loud because foundry professionals use jackhammer-like tools to break apart the shells, freeing the castings for final steps in the process.
The known history of investment casting goes back 5,000 years, to the early processes in Egypt and China. While it was extensively used through the ages, it entered the modern era in 19th century, when processes became more advanced and could be used for an array of purposes, including dentistry. Investment casting rapidly progressed and grew during World War II to meet the massive demand and produce products made of special alloys. Today, investment casting is an invaluable process utilizing advanced technology and equipment to produce a nearly endless variety of parts for all kinds of applications.
If you require precision cast parts that meet exacting specifications and extreme consistency, you should consider a foundry that has a full metallurgical lab onsite. This is especially important if your parts are made from uncommon alloys that take special expertise and knowledge. Ensuring that castings meet specifications and quality standards during production runs will eliminate substandard parts, reduce delays and save cost.
When employing the investment casting process to make precision cast parts, it is important to use precise tooling to ensure that the castings meet rigorous standards and specifications. The tooling is used to produce wax patterns that hold the exact dimensions of the desired parts as the ceramic molds are being made. Any inaccuracies in the tooling will be seen in the end castings. High quality, dependable tooling is an excellent investment.
For a quarter of a century, Donald “Butch” Sands has been doing the behind-the-scenes work that keeps foundries operating smoothly and efficiently. He came to PPCP in 1990 and is now a process control technician responsible for sampling all new jobs through the shop, participating in quoting and much more. One of his most important activities was leading the introduction of aluminum alloys to the PPCP casting materials list. Butch is a true professional who gets things done.
Investment casting is an excellent process for producing a nearly endless variety of specialized hardware. Unique and often complex hardware items for architecture, construction, medical, energy industry and many other applications can require the high-quality, near-net-shape capabilities of investment casting. It can also produce high quantities and large size parts consistently and cost effectively.
While investment casting seems straightforward on the surface, the process requires a great deal of expertise and experience. The metallurgy, science and process knowledge involved in producing high-quality, consistent castings is quite complex. A foundry without the necessary resources can encounter an array of issues that compromise the parts they produce. Among the key defects that can occur are porosity, poor surface finish, distortion, incomplete casting and voids in castings.
For many applications there are multiple casting processes that can be employed. If sand casting is currently being utilized, it can be beneficial to consider other options, such as investment casting. Investment casting is most likely a better choice if the application requires: high quantities of parts, thin part walls, small dimensional tolerances, high quality surface finishes and complex part geometries.
To ensure that investment castings achieve the required quality and performance specifications, a foundry should meet or exceed a variety of industry standards. While there are many more, PPCP conforms to the following: American National Standards Institute (ANSI), ASTM International, American Welding Society (AWS) and Aerospace Material Specifications (AMS).
RMS (Root Mean Square) and Ra (Roughness Average) are both measures of surface roughness. RMS calculates the Root Mean Square of the surface’s microscopic peaks and valleys. Ra takes the average of the peaks and valleys. They use the same height measurements. The RMS value will be affected more by a single or few large peaks (flaws) than will the Ra value.
Charpy impact testing is used by investment casting foundries to determine whether an alloy can be classified as ductile or brittle. This information is important for assessing the quality and properties of a casting. In the Charpy impact testing method, a standard notched sample is struck with a specific weight pendulum raised to a predetermined height. By measuring the energy absorbed when fracturing the sample, toughness of the test material can be determined. Alloys that require more energy to be fractured are more ductile. The nature of the fracture can also provide useful information about the alloy’s properties.
Ductile iron offers excellent properties for numerous applications and parts produced through the investment casting process. The structure and composition of ductile iron can produce parts with precise definition that virtually eliminates the need for machining and extensive finishing. It is also reasonably resistant to corrosion compared to some other alloys. Ductile iron can be used in diverse industries and applications, from petrochemicals, mining and railways to pumps, valves, hydro, architectural and more.
The specialized instruments and equipment utilized in the medical and dental profession require exceptional accuracy that can be achieved by precision cast parts. The near-net-shape of investment castings can deliver the exacting specifications and consistency that is crucial for an array medical and healthcare applications. In addition to the reliability and accuracy of precision cast parts, investment casting can also use a very broad range of alloys with properties that meet special needs. It is important to work with a foundry that has the expertise and resources to meet these needs.
Investment cast is an excellent process for producing the precision cast parts needed for military and defense applications. It offers the ability to economically cast highly accurate, complex parts out of an extensive range of specialized alloys. It also provides design flexibility and numerous other advantages, including the consistent, reliable quality the military requires.
Many controllable factors affect the quality of investment castings including the dryness of the ceramic shell, which becomes the casting mold. After the wax patterns are dipped into the slurry, they must be allowed to dry to an optimal point for the specific castings that are being made. Minimum drying times must be established taking into account the ambient temperature and humidity, as well as air flow from fans. These factors can be adjusted to establish drying times that optimize the casting workflow and quality.
Do you have a question related to commercial precision casting or PPCP? We have (almost all) the answers. You can submit your question anywhere on PPCP’s website through the “Ask a Question” feature. Just say who you are, where you are from, how to reach you, and what you want to know. A PPCP representative will get back to you within 24 hours, Monday through Friday. Or feel free to give us a call and we will be happy to help.
Producing high-quality parts that meet critical size specifications requires careful planning and production expertise in the investment casting process. After molten alloys are poured into molds they shrink as they cool. The dimensions of the finished castings will be smaller than the molds that form them. As a result, foundry professionals must take this shrinkage into account when designing the patterns. This can be quite complex because different alloys have different shrinkage allowances. In addition, any surface finishing can also affect the size, though this is minimal with investment casting.
If you are planning a commercial precision casting project, PPCP can help by providing a preliminary casting price quote. It’s quick and easy, and can be done right on our website in just a few moments. Just fill out the needed information, attach a design or specifications file, if available, and hit send. PPCP will get back to you ASAP with the information you need to plan your project. It will also expedite getting started with production of the top-quality, precision cast parts you need.
Many foundry professionals at PPCP play key roles in ensuring the quality and precision of the castings produced, but none more than Jacob Boylen. As a Process Control Technician, Jacob monitors and improves the production process. He also updates the Quality Assurance Display System, assists customers and much more. Jacob has been a valued member of the PPCP team since 2013.
One of the real advantages of the investment casting process is the ability to produce complex parts with little or no machining. Because it is a “near-net-shape” process, it can produce precision castings that even have flawless right angles and other intricacies right out of the mold. Once the molten alloy has cooled, the shell or mold can be broken off of the parts during the knockoff process. In the vast majority of cases, it’s ready to go as-is or with only minor finishing. That saves significant cost and time, and produces better parts.
A key factor in ensuring the quality of precision castings is the quality of the slurry – the ceramic that covers patterns to create investment casting molds. To begin, the proper slurry formula must be used for the application, and it must be mixed in the appropriate manner. Once the slurry is made, it will have a finite life, after which it will not perform optimally. A variety of factors can degrade the slurry, especially water loss, which changes the viscosity and can compromise the mold strength. Experience and advanced capabilities are necessary to ensure that the slurry, the molds and the castings are optimal.
While sand casting can be an appropriate process in a variety of applications, investment casting offers significant advantages, due in large part to the versatility of its mold. With sand casting, molds must be pulled apart to remove the pattern before pouring the molten alloy. These molds use a cope and drag to make a box container that is filled with sand, surrounding the solid pattern. There is always a “parting line” that must be ground off with sand molds because they are made from two pieces. In addition, sand casting must utilize a preformed core within the mold, which adds complexity. Also, sand molds simply cannot achieve the hardness of ceramic, which can compromise the surface finish and tolerances. These issues can all be avoided with investment casting’s wax patterns and ceramic molds.
Stainless steel can be an ideal material for parts and applications that require a stain- and rust-resistant surface. It is made of iron, chromium (which gives it a non-reactive characteristic) and in many cases an array of other components, including silicon, nickel, carbon, nitrogen and manganese. There are currently dozens of recognized stainless steel alloys, plus a nearly endless variety of custom formulas. Addressing the complexity and characteristics of stainless steel alloys in a foundry requires specialized knowledge and experience—like that found at PPCP.
Investment casting is one of the most versatile processes for producing parts from a wide variety of materials. From ductile iron and stainless steel to aluminum and super-alloys, virtually no other process can accommodate as many alloys and materials. It out-performs other forms of casting, forging, stamping, extrusion, permanent molding and more. Each of these other processes can be preferred for certain applications and situations, but across the board, investment casting is clearly best.
Cobalt-chromium alloys offer attractive properties for specialized applications. To achieve the desired performance, the composition of these alloys can be adjusted as needed. Because they can be used in the investment casting process, parts made with cobalt-chromium alloys also offer the advantages of high-quality, near-net-shape casting. Cobalt-chromium alloys generally provide high resistance to wear, galling and corrosion and retain these properties at high temperatures. Their hardness, durability and lack of malleability make them excellent for cutting tools and similar applications in a wide variety of industries.
Ensuring the quality, performance and specifications of the parts PPCP casts is a critically important part of the process. Kenny Achenbach, Lab Manager, is the man who makes it happen. As the “heart and soul of our materials oversight,” Ken is responsible for the lab where metals are analyzed and the chemical and mechanical properties of every heat of metal poured at PPCP are recorded. He uses advanced testing technology deliver what PPCP promises. Ken has been part of the PPP team since 1991. Read more about the skilled people of PPCP.
Aluminum is an excellent metal to use for investment casting because of its many favorable properties, from being lightweight and durable to non-corrosive and highly workable. It can be utilized in numerous alloys that can accommodate diverse applications and requirements. Here are some basic facts about aluminum:
- It is the third most abundant element in the Earth’s crust (about 8.8%), behind oxygen and silicon.
- It is naturally occurring only in compounds, and removing it from compounds is difficult. The first inexpensive process for obtaining pure aluminum was not developed until 1886.
- The melting point is 1,220 degrees Fahrenheit, which is considerably lower then many other metals commonly used in industrial applications.
- It is an excellent conductor of electricity.
- Aluminum naturally forms a very thin, whitish coating of aluminum oxide in moist air, which protects it from further reaction and corrosion, like rusting.
- Aluminum is highly flammable when in fine power form.
- Bauxite, a complex aluminum compound found in nature, accounts for over half of Jamaica’s exports and is the island country’s second largest industry after tourism.
- 28% of aluminum is used in transportation, 23% in packaging, 14% in building products and the remaining 35% in a nearly limitless array of products.
There are numerous factors to consider when choosing the right process for producing parts. While there may be special considerations and other issues, here are some important items to take into account:
- Application – how will the part be used? Are there special requirements?
- Alloy – does the application require a specialized alloy?
- Precision – how tight are the tolerances and specifications?
- Complexity – is the part design and configuration intricate, with fine work required?
- Mechanical – does it require assembly or finishing work?
- Quality – are there rigorous performance requirements?
- Quantity – how long are the production runs and how frequent?
- Longevity – will it be produced over a long period of time without design changes?
Choosing the right foundry, with the necessary expertise to help address all these issues is also very important.
If you are planning to produce metal castings up to 250 pounds, made from a wide array of alloys, Pennsylvania Precision Cast Parts is ready to offer a competitive quote. PPCP’s seasoned investment casting professionals will make the process quick and easy, while consistently delivering top-quality parts that meet your specifications and requirements. Just click here or on the Request a Quote button at the top of this page to get started.